Askjake Concrete

askjake Concrete

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Concrete on concrete

Concrete front porch & concrete back porch, both are not level & they hold water after a rain. Can new concrete go over the 3 year old concrete to level porches without any problems?

Thanks,

Otis

 

Otis,

As a rule, new concrete is not placed over old concrete.  The old concrete might be holding water due to improper grade preparation.  

Concrete, in our part of the country, is placed over crushed rock (gravel), usually a minimum of 4” with some sort of re-enforcement installed – either a 6 x 6 mesh or ½” rebar.  The gravel allows for excess water to drain away from the slab and to help the soil remain stable.  

If you have a “dip” in the slab and this dip is holding water, infilling the dip rarely solves the problem. Usually you will land up just relocating the dip to another area.  

Built-up coatings that re-level concrete rarely work in our area due to the affects of the freeze-thaw cycles we experience.  Bottom line – you will be best served in the long run to remove the slab and start over. 

Leveling basement concrete

Question from Mel : 

I have a concrete floor that is low in the middle by 6 or 7 inches i want to level it and put down some type of a wood floor. There is not a lot of over head space. Cost is a factor.

Mel, 

We have run into this same situation several times when finishing off a basement. 6 to 7 is a lot to level. I would start out by using a latex bonding agent on the existing concrete and then place a regular sack concrete mix and level the floor within 2 of level. Let this set up for 7 days before proceeding to the next step. To finish off the leveling, use a self-leveling mix over the new concrete. Check out quickcrete.com for some information about these types of products.

Cracked Slab

We found the home of our dreams. But it has a cracked slab that was repaired 2 years ago by a company that offers a lifetime warranty. The house is 27 years old. What is your opinion—is it a wise decision to buy a home with a cracked slab? It was repaired, but does that matter? Thanks so much! Jill

Jill,

When it comes to concrete, we only guarantee it against theft and fire. We can almost always guarantee that it will crack. Concrete can crack due to several reasons: faulty sub soil, poor drainage below the slab, poor quality concrete, concrete not placed and finished properly or poor weather conditions when it was installed. Is the slab cracked and separated? Is one side higher than the other? If there is reinforcement in the slab, such as re-bar or wire mesh, I probably would not worry about it. Does water seep through the crack? That would worry me. If the crack is wider than a 1/4 that would worry me. What is the life time guarantee to do? Good luck.

Crackin’ up

askjake Concrete

Jake,

I have a problem with my garage floor, Brad suggested that you may have some advice in addition to what has told me.

I have a crack in my garage floor that starts in the middle of one of the large doors and runs length ways the full length of the garage toward the outside and stops in the adjoining laundry room. This has been there for years but over the last two or three it has gradually started to crown around the garage door. When the door is closed I can see a small gap on both ends where the door meets the floor.

My question is can this be corrected? Who should I contact for a proper analysis? Brad said that I could try Alpha-Omega Geotech but he said Hiring an engineer can get expensive.

Ideally I would like to stop the movement and if possible get the floor back to where it was.

I would greatly appreciate any Ideals or contacts you could give me.

Thank You

Alan W

Alan,

You pose an interesting question. From your description of the problem, it sounds like the crack is crowning which must mean that the slab may be settling along the sides of the outside walls causing the middle to raise up. This could be occurring due to the settling that might be going on along side the foundation walls. This is not too uncommon since these areas were excavated for the foundation then backfilled. Did you string a line from one side of the floor to the other side across the crack to determine if it is actually crowning? If you find that there is a crown, you might have to mud jack along side the foundation to stabilize the slab. Mud jacking could raise the slabs which might remove the crown as well. I have seen the soil below garage and basement slabs be several inches below the bottom of the slabs, thus leaving the slab as a suspended slab. Look along the side the foundation walls to see if you can see the original slab pour line.

If none of the above is the case, let me know and we’ll see if there might be a Plan B.


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